GENERAL COGNITIVE ABILITY

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GENERAL COGNITIVE ABILITY
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GENERAL COGNITIVE ABILITY

• Cognitive abilities are organized in a
  hierarchical model from testable traits to
  general cognitive abilities
• Tests assess individual cognitive abilities that
  rendered reasonable indices of g
• g is derived from factor analysis in which tests
  are weighted differently in agreement to their
  contribution to g

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GENERAL COGNITIVE ABILITY

• A tests contribution to g is related to the
  complexity of cognitive operations it assesses
• g is one of the most reliable measures of
  behaviour
• It is quite consistent over life span
• It is related to social and educational outcomes
• It is substantially heritable

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GENERAL COGNITIVE ABILITYHistorical highlights

• Galton
• Invented correlation
• First systematic studies showing that behavioural
  traits run in families
• there is no escape from the conclusion that
  nature prevails enourmously over nurture
• First twin study focused on g

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GENERAL COGNITIVE ABILITYHistorical highlights

• 1924 Tolman followed by Tryon
• rats bred for their performance in learning a
  maze to find food
• No overlap between breeds
• No increased difference after a few generations
• Coper and Zubek, 1958
• Different breeds under enriched, normal and
  restricted environments.
• Brights dulls in restricted environment while
  dull bright in enriched environments
• Other studies failed to find evidence of
  gene-environment interactions

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GENERAL COGNITIVE ABILITYHistorical highlights

• Many studies between 50s and 60s using inbred
  mice showed important contributions of genetics
  in several learning situations.
• g accounted for 61 of variance for inbred mice
  and 55 for outbred mice
• More complex tasks show better the influence of g
  in comparison to simpler tasks

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GENERAL COGNITIVE ABILITYHuman studies

• Burks (1928) and Leahy (1935) showed that IQ
  correlations were greater in nonadoptive than in
  adoptive families
• Burt (1966) MZ twins reared appart are very
  similar to MZ twins reared together but his data
  is dubious
• Jensen (1969) etnic differences in IQ might
  involve genetic differences (The bell curve)
• The causes of average differences between groups
  need not to be related to those of individual
  differences within groups
• 80s genetic differences amongst individuals are
  significantly associated with differences in g

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GENERAL COGNITIVE ABILITYGenetic influence

• A bit of bad genetic influence http//www.dnai.org
  /lesson/go/7687/7130

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GENERAL COGNITIVE ABILITYGenetic influence

• Heritability is as high as 52 percent when
  derived from twin correlations
• When controlling for unreliability of measure
  heritability is higher
• Heritability appears high across cultures

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GENERAL COGNITIVE ABILITYEnvironmental influence

• A third of total variance is explained by shared
  environment
• Shared environment accounts for less resemblance
  between parents and offspring than between
  siblings
• Correlation for relative living together are
  higher than for relatives living apart
• Shared environments contribute more to the
  resemblance of twins than to that of non-twins
• Role of shared environment for g 20 P-O, 25
  siblings and 40 twins

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GENERAL COGNITIVE ABILITYAssortative mating

• Non random mating
• Individuals who mate tend to be similar
• Correlations amongst spouses are .25 for height
  and .20 for weight, .6 for education and .6 for g
  but only .1 to .2 for personality
• Increases genetic variance in a population and
  its effects accumulate generation after
  generation
• It increases heritability by making first degree
  relatives more similar to each other
• For twin studies it decreases heritability
  because DZ have more similarities
• It could be confounded as shared environment
  influence

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GENERAL COGNITIVE ABILITYAdditive and
non-additive genetic variance

• Additive effects Alleles at a locus and across
  loci add up to affect behaviour
• The contribution of an allele to phenotype is the
  same for parent and offspring increasing their
  resemblance
• Additive effects make us resemble our parents
• Dominance deviation alleles interact but do not
  add up
• Dominance deviation is the difference between
  genotypic values and expected values under an
  additive model
• Dominant effects make us be different from our
  parents

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GENERAL COGNITIVE ABILITYAdditive and
non-additive genetic variance

• Polygenic Models
• Many genes could add up or interact to produce a
  phenotype
• Interactions between alleles at different loci is
  called epistasis
• Due to epistasis two alleles may not result in
  two more points (additive) but in ten more points
• Total genetic contribution is G
• G A D I
• Extreme forms of epistasis is called emergenesis.
  It consists in extraordinary effects of unique
  combinations of alleles

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GENERAL COGNITIVE ABILITYAdditive and
non-additive genetic variance

• For g effects are largely additive
• Assortative mating masks some non additive
  genetic variance because it increases
  similarities
• Dominance is more obvious in inbreed populations
• It reduces heterozygocity by increasing dominant
  and recessive homozygotes
• Inbreeding decreased IQ

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GENERAL COGNITIVE ABILITYDevelopment

• For g genetic factors become more important as
  time goes by
• p-o correlations increase with time
• DZ twin correlations decrease compared with that
  of MZ which remain stable
• Heritability for reared together vs appart MZ
  twins was 80
• Small genetic effects may snowball during
  development
• Shared environment effects are less important in
  adulthood
• G could be rescued
• Non related adoptive children resemble each
  other but the similarities are lost in adulthood
  as correlations in g decline (shared environment)
• Genetic effects differ from one age to the other

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GENERAL COGNITIVE ABILITYlooking for genes

• More than 100 single gene disorders cause mental
  retardation
• Not all of them do so in a 1/0 fashion
• Strategies used candidate gene, genome scans and
  DNA pooling

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Specific Cognitive Abilities

• Specific cognitive abilities show slightly less
  genetic influence than g
• Memory and verbal fluency are show the least
• Verbal and spatial ability show the highest